PORPHYRIN BIOSYNTHESIS IN ERYTHROCYTES

Delta-Aminolevulinic Acid-Mediated Photodiagnoses in Surgical Oncology: A Historical Review of Clinical Trials

Fluorescence imaging is an emerging clinical technique for real-time intraoperative visualization of tumors and their boundaries. Though multiple fluorescent contrast agents are available in the basic sciences, few fluorescence agents are available for clinical use. Of the clinical fluorophores, delta aminolevulinic acid (5ALA) is unique for generating visible wavelength tumor-specific fluorescence. In 2017, 5ALA was FDA-approved for glioma surgery in the United States. Additionally, clinical studies suggest this agent may have utility in surgical subspecialties outside of neurosurgery. Data from dermatology, OB/GYN, urology, cardiothoracic surgery, and gastrointestinal surgery show 5ALA is helpful for intraoperative visualization of malignant tissues in multiple organ systems. This review summarizes data from English-language 5ALA clinical trials across surgical subspecialties. Imaging systems, routes of administration, dosing, efficacy, and related side effects are reviewed. We found that modified surgical microscopes and endoscopes are the preferred imaging devices. Systemic dosing across surgical specialties range between 5 and 30 mg/kg bodyweight. Multiple studies discussed potential for skin irritation with sun exposure, however this side effect is infrequently reported. Overall, 5ALA has shown high sensitivity for labeling malignant tissues and providing a means to visualize malignant tissue not apparent with standard operative light sources.

Uroporphyrinogen decarboxylation as a benchmark for the catalytic proficiency of enzymes

The magnitude of an enzyme's affinity for the altered substrate in the transition state exceeds its affinity for the substrate in the ground state by a factor matching the rate enhancement that the enzyme produces. Particularly remarkable are those enzymes that act as simple protein catalysts, without the assistance of metals or other cofactors. To determine the extent to which one such enzyme, human uroporphyrinogen decarboxylase, enhances the rate of substrate decarboxylation, we examined the rate of spontaneous decarboxylation of pyrrolyl-3-acetate. Extrapolation of first-order rate constants measured at elevated temperatures indicates that this reaction proceeds with a half-life of 2.3 x 10(9) years at 25 degrees C in the absence of enzyme. This enzyme shows no significant homology with orotidine 5'-monophosphate decarboxylase (ODCase), another cofactorless enzyme that catalyzes a very slow reaction. It is proposed that, in both cases, a protonated basic residue (Arg-37 in the case of human UroD; Lys-93 in the case of yeast ODCase) furnishes a counterion that helps the scissile carboxylate group of the substrate leave water and enter a relatively nonpolar environment, stabilizes the incipient carbanion generated by the departure of CO(2), and supplies the proton that takes its place.

Inhibition studies of porphobilinogen synthase from Escherichia coli differentiating between the two recognition sites

Porphobilinogen synthase condenses two molecules of 5-aminolevulinate in an asymmetric way. This unusual transformation requires a selective recognition and differentiation between the substrates ending up in the A site or in the P site of porphobilinogen synthase. Studies of inhibitors based on the key intermediate first postulated by Jordan allowed differentiation of the two recognition sites. The P site, whose structure is known from X-ray crystallographic studies, tolerates ester functions well. The A site interacts very strongly with nitro groups, but is not very tolerant to ester functions. This differentiation is a central factor in the asymmetric handling of the two identical substrates. Finally, it could be shown that the keto group of the substrate bound at the A site is not only essential for the recognition, but that an increase in electrophilicity of the carbon atom also increases the inhibition potency considerably. This has important consequences for the recognition process at the A site, whose exact structure is not yet known.

CHARACTERIZATION OF THE PIGMENT OF MICROCOCCUS VIOLAGABRIELLAE

Production of the red insoluble pigment by Micrococcus violagabriellae was studied. Pigmentation was found to require oxygen and high levels of iron and to be stimulated by tryptophan alone among the amino acids. The pigment was isolated, purified, and analyzed chemically and spectrophotometrically. It was found to be similar to pulcherrimin from Candida pulcherrima. Immunological cross reactivity and analysis of derivatives confirmed the similarity between the bacterial and yeast pigments. From these data it is postulated that the pigment is an iron chelate of pulcherriminic acid with an associated low molecular weight peptide moiety with glycine as the sole N-terminal amino acid. The pigment appears to differ from that of C. pulcherrima solely with respect to this peptide and in the mode of aggregation of the molecule.